Method of making crinkled fibers



IN V EN TOR. Ale/son W Abe/"0611 4 N. W. ABERNETHY METHOD OF MAKING CRINKLED FIBERS Flled Sept 18 1948 ATTORNEYS Feb. 27, 1951 and Feb. 21, 1951 METHOD OF MAKING OEINKLED FIBERS Nelson W. Abernethy. Midland, Mich., assignor to The Dow Chemical Company, Midland, a corporation of Delaware Mich Application September 18, 1948, Serial No. 49,871 4 Claims. (CL 18-54) 1 This invention relates to a method of making crinkled fibers from extrudable organic thermoplastics. It relates in particular to a method for making crinkled fibers from extrudable normally crystalline sarans.

The normally crystalline sarans are those polymeric and copolymeric compositions of vinylidene chloride which normally exhibit characteristic crystal patterns when examined by X-ray diffraction methods. In common with other extrudable thermoplastics, it is desirable to be ableto produce crinkled, i. e., kinked, curled, wavy or wool-like, filaments or fibers from the sarans. Several types of crimping methods are known and have been applied to various filaments in attempts to produce the desired effects. Mechanical crimping operations, in which the fibers are passed between knurled rolls, are unsatisfactory in many cases because of the too obvious uniformity of the crimps, and in other cases because the heat and pressure used in crimping, distort the filaments out of round. Chemical treatments have been applied to some fibers to effect crinkling by subjecting portions of the fiber to greater stresses than others. Such methods depend largely on the ability of the treating agent to swell or distort thefilament, and, because of the high resistance of the crystalline sarans to attack by most chemicals and solvents, these methods are not generally applicable to or effective with saran.

A method of crinkling saran filaments was disclosed by Robbins in U. S. 2,377,810, which consisted in directing a mist of a non-solvent liquid upon but one side of the freshly extruded hot filament, supercooling the so-treated product, and cold-stretching it. Robbins reported that lessfavorable results were obtained when a gas was employed instead of a liquid in his process. It would be preferable, however, to avoid necessity for using and maintaining a liquid spray.

during the extrusion operations. It would be desirable, as well, to be able-to produce any desired degree of crinkle in saran or other extrudable organic thermoplastic by a simple technic which can be applied wherever such plastics can be extruded and without special knowledge as to the chemical characteristics of the filaments to be treated.

It is the principal object of the present invention to provide a simple process for the preparation of crinkled filaments from extrudable organic thermoplastlcs. A particular object is to provide such a method whereby saran filaments may be produced having any desired degree of crinkle. A related object is to provide such a process in which there is no interference with or interruption of the normal extrusion operation whereby the filaments are obtained.

According to the present invention, the foregoing objects are attained by carrying out the normal extrusion and stretching operation as employed for preparing straight and uncrinkled filaments from an extrudable organic thermoplastic while directing against all sides of each extruded filament a plurality of controlled streams of air or other inert gas at a point between 1 and 10 inches outside the extrusion orifice. Because the entire shell of each filament, and not one side only, is cooled somewhat by the air streams, and there is a uniform differential between temperatures of the fiber shell and core, the resulting crinkled filament is more uniform than any produced by spraying or blowing on but one side of the filaments.

The invention will be described more fully with reference to the accompanying drawing, Fig. 1 of which illustrates one apparatus for carrying out the method of the invention, while Fig. 2 is a view in the vertical plane through line 2-2 of Fig. l, and Fig. 3 is a plan view in the horizontal plane through line 3-3 of Fig. 2.

Referring now to the drawings, one or a plurality of filaments III of an organic thermoplastic may be extruded under normal conditions from the orifices of a standard plastics extruder II. Filaments I0 pass downwardly, while still hot, through a zone surrounded by gas nozzles l2 directed toward the filaments l0 and tilted slightly upward so that streams of air or gas converge in an air cone with its apex in the center of the cluster of filaments l0 slightly above the plane of the nozzles 12, and pass out through the cluster again, touching the other surfaces of filaments Inat a still higher level, as illustrated by dotted lines in Fig. 2. This disposition of nozzles l2 prevents the air streams from forcing the filaments in into contact with one another while still hot and cohesive. Having passed through the multiple air streams from nozzles 12, the filaments [0 are passed around suitable guide rolls l3 and M in standard manner and thence around snubbing rolls l5 which serve both to stretch the hot filaments in the zone between the extruder II and guide roll l3 and to prevent transmission back to that zone of any additional stretching force applied by rolls l6 around which the filaments I0 are passed between snubbers l5 and a winding reel l1. When the filaments ID are composed of normally crystalline vinylidene chloride polymer, they are passed through a bath of cold water IE or other inert liquid to supercool them before they are coldstretched up to about 400 per cent between rolls I5 and IE to effect recrystallization and orientation. After leaving rolls l6, filaments treated in the manner described have a natural and permanent crinkle, and may be wound on a storage reel ll, as illustrated, or they may be passed directly to a cutter (not shown) for the preparation of short staple fibers.

The multiple gas nozzles 12 may be in several separate assemblies, but a more convenient and practical arrangement is that shown, in which a tubular ring It serves as a header for all nossles l2 and receives air or other gas under slight pressure through inlet pipe 20. Ring Is is easily disposed concentric with and in a plane .essentially vertical to the descending cluster of filaments Ill. The level of ring I! may be altered at will so that the air streams pass over the filaments In at distances ranging from 2 inches to or more inches from the extruder I l It has been found that the degree of crinkle imparted to the final stretched filaments is increased as the level of contact between the filaments l0 and the air streams approaches extruder II and is decreased as that level becomes more distant from the orifice. It has also been found that the degree of hot stretch imparted to filaments it above guide roll it (or above supercooling bath It, in the case of saran filaments), and the degree of cold stretch of saran filaments between rolls II and I8, are directly proportional to the tightness of the kink found in the final product. Another observation is that the temperature of the gas or air blown through nozzles l2 upon the hot filaments I0 is not esp cially important but that air at or near room temperature appears to exert a slightly greater crinkling action on the filaments, under otherwise standard conditions than does chilled air or heated air.

In a series of illustrative examples, a plasticized normally crystalline-copolymer of vinylidene chloride and vinyl chloride, having a melting point of 173 C. was extruded at that temperature at a rate of about grams per minute through a die having 30 orifices each 0.018 inch in diameter and disposed in a circle 0.5 inch in diameter. The resulting filaments dropped 30 inches into a supercooling bath of water at 25 C., and were passed around the illustrated rolls l3, H and IS. The latter rolls operated at a peripheral speed of about 200 feet per minute, except as is noted in Table 11, below, and reduced the diameter of the filaments in the hot zone near the extruder. Cold-stretching rolls I6 operated at peripheral speeds of about 3.75 times those of rolls I5, and further reduced the denier of the fibers. The hot filaments passed through a 4-inch ring of 0.25 inch tubing perforated as shown in Figs. 2 and 3,

to provide 16 holes 0.063 inch in diameter positioned so that streams of air discharged therefrom converged about 2 inches above the level of the ring. In passing through the air cone, the filaments were in the main air streams for a distance of about one inch and were subjected substantially uniformly to the efiects of those streams about their peripheries. It was found that, other factors being constant, the degree of kinking or curling in the filaments varied directly with the velocity of the air streams.

Table I Eflect of distance of air ring from extrusion die Distance Distance,

air ring apex of Degree of crinkle in to die, air cone to filaments inches die, inches 3 1 V tight kinks.

6 4 Good curl.

9 7 Waves.

i2 10 Slight waves.

' the inert gas is air at about room temperature.

Table II sweet of speed of take-away on degree of crinkle as: Pitt D a... i.

0 to die, laments inches mu a We 3 G crinkle. a 345 Tight kinks. a 440 Very tight 1am.

Table III Eflect of air temperature on degree of crinkle Tam mm D so of crinkle 13;??? in filaments 5 Loose kinks. 24 Tight kinks. 61 Loose kinks.

In each of the foregoing tables, all conditions except those noted were kept constant.

Similar results have been noted when operating on all extrudable compositions of the normally crystalline polymer and copolymer of vinylidene chloride.

I claim: 1

1. The method whichcomprises extruding fine filaments of a normally crystalline saran downwardly through air and directing against all sidesof each such filament a plurality of streams of a gas inert to the filaments at a level between 1 and 10 inches outside the extrusion orifice and in a manner such as not to force the hot filaments into coherence with one another, and supercooling and stretching the filaments, to obtain a filamentary product having a natural crinkle.

2. The method which comprises extruding fine filaments of a normally crystalline saran downwardly through air and directing against all sides of each such filament a, plurality of streams of a gasinert to the filaments, said streams converging upwardly to define a cone with its apex from 1 to 10 inches beneath the extrusion orifice, and supercooling and stretching the filaments, to obtain a filamentary product having a natural crinkle.

3. The method as claimed in claim 1, wherein 4. The method as claimed in claim 2, wherein the inert gas is air at about room temperature.

NELSON W. ABERNETHY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. THE METHOD WHICH COMPRISES EXTRUDING FINE FILAMENTS OF A NORMALLY CRYSTALLINE SARAN DOWNWARDLY THROUGH AIR AND DIRECTING AGAINST ALL SIDES OF EACH SUCH FILAMENT A PLURALITY OF STREAMS OF AA GAS INERT TO THE FILAMENTS AT A LEVEL BETWEEN 1 AND 10 INCHES OUTSIDE THE EXTRUSION OFIRICE AND IN A MANNER SUCH AS NOT TO FORCE THE HOT FILAMENTS INTO COHERENCE WITH ONE ANOTHER, AND SUPERCOOLING AND STRETCHING THE FILAMENTS, TO OBTIAN A FILAMENTARY PRODUCT HAVING A NATURAL CRINKLE. 